The subject of the present invention is a heat-modified starch.
Starch is the principal carbohydrate component of higher plants. It includes 98-99%, of a carbohydrate fraction which is a mixture of amylose and amylopectin. At room temperature, native starch granules are insoluble in water. This insolubility is attributed to the crystalline organization of starch. Starch is only of low industrial interest in this case. By hydrothermal treatment, or by gelatinization, this crystalline organization is destroyed and starch finds numerous industrial applications.
In the food sector, native or modified starches are used as texturing agents, as thickeners, as gelling agents or as stabilizers. However, certain food technologies require starches having specific properties, such as shear strength, viscometric stability, preservation of viscosity in acid medium, delayed gelatinization or satisfactory heat transfer during sterilization.
Moreover, in the face of the innovations in the food technology sector, it is necessary to have available thickeners having not only predictable behavior, but also controllable behavior.
A varied choice of modified starches exists depending on the raw material, the treatment carried out and its intensity.
Thus, EP 0,710,670 describes a process for the preparation of a chemically modified starch as well as the apparatus which makes it possible to chemically modify this starch. In the process, a starch, having a water content of 9-25%, is chemically treated in a turbo-reactor, at 300-1500 rpm and at acidic pH, in the presence of a modifying agent, such as, for example, an alkylating agent or an acylating agent.
However, in the food sector, the use of chemically modified starches is regulated and should appear on the product packaging. Physical modifications make it possible to avoid these constraints.
Accordingly, U.S. Pat. No. 4,508,576 describes a process for the preparation of a maize starch which is dispersible in boiling water at 5% and which has a high viscosity level of 2000 centipoises at 70.degree. C. In this process, a mixture having a water content of 43-50% and containing maize starch granules and an emulsifier, such as glycerol monostearate, sorbitol and propylene oxide, is microwave-heated at 50-85.degree. C. for 1 h so as to reduce the water content to 15%.
Moreover, EP 0,150,715 describes a process for the preparation of a starch which is dispersible in boiling water at 95-100%. In this process, a mixture having a water content of 20-30% by weight and containing starch, 1-5% of emulsifiers, relative to the dry weight of the starch, and water, is heat-treated with microwaves at 90-120.degree. C. for 1-20 min.
Finally, Societe Roquette Freres S. A., 4 rue Patou, F-59022 LILLE, markets a starch, under the name of Cremalys, having a gelatinization temperature of 83.degree. C., but not having sufficient viscostability, that is to say that the increase in the viscosity of this starch on cooling is high.